【作者】 张俊婷；

【导师】 崔小朝；

【作者基本信息】 太原科技大学 ， 工程力学， 2008， 硕士

【摘要】 本论文提出了一种低过热度浇注技术,即“通过旋转的冷却辊将液态金属冷却,并强迫其注入结晶器”,为有效解决低过热度浇铸工艺带来的水口堵塞问题提出了一种新方法。利用CFD商用软件Fluent分别对双辊冷却低过热度浇铸方坯连铸和薄板坯连铸结晶器内钢水的流场、温度场及凝固场在不同拉速情况下做了模拟与分析,并与浸入式水口浇铸下结晶器内钢水的流动及凝固状况进行了比较。为验证双辊冷却低过热度浇铸对改善铸坯组织的有效性,以99%的工业铝为实验材料,研究了经“U”型管冷却的铝液在低过热度浇铸下铝锭铸坯的宏观组织及力学性能。论文研究结果表明:(1)钢液经冷却辊冷却浇入结晶器内,由于冷却辊对浇铸钢液起到了冷却作用,过热度变小,实现了低过热度浇铸的目的。随着拉速的提高,冷却辊的冷却作用相对变小。(2)流场分析表明钢液经冷却辊注入结晶器形成向下的冲击流,一方面该冲击流有利于打断凝固前沿的柱状晶,从而形成新的形核驱动力,扩大等轴晶率;另一方面冲击流冲击到一定深度产生上旋回流涡,该回流涡有利于钢液中夹杂物的去除和保护渣的熔化。(3)双辊冷却浇铸与浸入式水口浇铸相比,结晶器内钢液的温度场分布、凝固壳生长均均匀,且温度梯度小、液固两相区宽,有利于提高等轴晶率,抑制柱状晶的生长;同时可降低铸坯凝固组织中的中心偏析、疏松以及裂纹等缺陷的产生。(4)以工业铝为实验材料进行实验研究,结果表明低过热度浇铸下铝铸锭的宏观组织得到了改善和细化,且铝铸件的强度极限得到了较为显著的提高。更多还原

【Abstract】 A kind of low superheat forces pouring technology is introduced in this paper, that is, the liquid metal is poured into mould by cooling roller, a new approach is introduced to solve the problem of water mouth blinding in low-superheat casting technology. By the aid of CFD business software—Fluent, flow field, temperature field and solidification field of the molten steel in mould are simulated and analyzed for billet casting mold and thin slabs casting mold poured by two rollers cooling in low superheat at different pull velocity. At the same time, the conclusion is compared with the flow-state and solidification of the molten steel in mould with immersion water mouth poured. Finally, in order to verify the validity of simulation data, the macro organization and mechanics characters of aluminum ingot which is cooled through“U”pipe at low superheat casting are studied for the experimental material of 99% industrial aluminum. The conclusion in the paper show:(1) For the refrigeration by cooling roller, the steel liquid is poured into mould realizing the purpose of casting at lower superheat. As the increasing of pull velocity, the cooling roller actions play down relatively.(2) Flow field shows that steel liquid is poured into mould by cooling roller and form shock stream downward. On the one hand, the shock stream breaks up the syllogistic crystal of solidification front, then the new driving force will be formed and the isometric crystal rate will be enlarged. On the other hand, the shock stream brings convolute backset at certain depth, which is helpful to exclude the field trash in steel liquid and melt the protecting dregs.(3) Compared with immersion water mouth casting, the distribution of temperature field and the growing of solidification shell of the steel liquid in mould by two rollers cooling casting at low superheat are uniform. Moreover, the steel liquid in mould by two rollers cooling casting at low superheat has little gradient of temperature and wide two-phase district of liquid and solid. It is favorable to raise paraxial crystal rate, inhibit syllogistic crystal growth, and degrade center-segregation, defect rate of loose and slight crackle in the organization of casting slab.(4) With the experimental material of industrial aluminum, the result shows that macro organization of the aluminum ingot casting by cooling rollers at low superheat is improved and its ultimate stress is refined greatly.更多还原